Reviews and Book N^otices. 123 



other minerals are in this case scattered more or less uniformly 

 throug-h the mass (Plate XI.,). The boundaries of the cordierite 

 grains are invisible in natural lig'ht, but become very evident 

 with crossed nicols. 



When larg-e crystals of aluminous silicates are formed in 

 slates which contain carbonaceous matter, the finely divided 

 opaque inclusions often tend to arrang-e themselves in a definite 

 manner. The most familiar example of this is the chiastolite 

 variety of andalusite, which is well shown in many of the 

 Skiddaw rocks. An analog^ous micro-structure is sometimes 

 met with in staurolite. In cordierite any special arrangement 

 of the carbonaceous inclusions seems to be rare, and I have seen 

 it only in one localitv, near the farm of Swineside in the lower 

 part of the Caldew valley.* The cordierite in all these rocks is 

 usually fresh, but in some cases the marg-inal part of a crystal 

 is altered into an ag"g"regate of minute flakes of a colourless 

 micaceous mineral. 



Summarily, cordierite is of very widespread occurrence in 

 the metamorphosed slates surroundings the Skiddaw g-ranite. 

 So far as my examination g"oes, it is rarely absent, except in 

 some of the more g-ritty beds, and it is often the principal con- 

 stituent of the completely metamorphosed rocks. If Ward saw 

 it, he perhaps mistook it for andalusite ; but cordierite was 

 probably absent from the examples which he studied more 

 particularly, for, according" to the chemical analyses, these 

 ■contained only about two per cent, of mag"nesia. The specimens 

 which I have examined came from the Caldew Valley and its 

 neig'hbourhood, including- Poddy Gill, Grains Gill, Burdell Gill, 

 .&c. ; also from Lonscale Fell, Dash, and Sinen Gill. 



Six Lemons de Prehistoire. Par Georges Engerrand. Bnixelles 

 Imp. Veuve Ferd. Larcier. 263 pag'es, and 124 figfures in the text. 



In this little volume the author gives a useful summary of our know- 

 ledge of prehistoric man on the continent, under the heads of ' General 

 Considerations,' ' Tertiar}- Man,' 'The Eoliths,' 'The Lower Paleolithic 

 Ag'e," 'The Upper Palaeolithic Age,' and 'The Neolithic Period.' Through- 

 out, the work is profusely illustrated, almost every possible point being" 

 explained by a sketch or diagram. Some of these however are rather 

 crude. There is a very good index. W'c should have preferred a much 

 more substantial cover to the book— a paper covered book rarely reaches 

 this countrv intact. 



* .See fig., Geul. Mag., '<594, p. 169. 

 igo6 April i. 



